Is your water green and clear, or green and cloudy? If it's green and clear, it's possible that you have metal staining. If you have copper or iron in your fill water, the shocking would have dropped it out of solution in the form of stains, which can make the water appear green--copper usually causes greenish stains, iron can make yellowish stains. If it's green and cloudy, then odds are you haven't killed the algae yet, and you need to bring your chlorine levels back up to shock level ( 15 ppm for a CYA of 50) and hold it there until the pool clears up.